Intracellular Ca2+ plays a fundamental role in many cellular processes including proliferation, differentiation, and muscle contraction/relation. he sarcoplasmic/endoplasmic reticulum Ca2+ transport ATPase (SERCAs) are key enzymes involved in the regulation of cytoplasmic Ca2+ and intracellular Ca2_ stores. Alterations in SERCA expression and/or function can occur under certain physiological or pathophysiological conditions including hypertension and heart failure. Specific inhibitors of the SERCA pump are increasingly being used to study: (1) intracellular Ca2+ homeostasis, (2) regulation of SERCA gene expression, and (3) structure-function relationships within SERCA. We have developed a novel model system based on these SERCA pump inhibitors, which forms the basis for the current application. In particular, we have developed, under various selection strategies, mammalian cell lines that are highly resistant to the inhibitor effects of the specific SERCA pump blockers thapsigargin (TG) and 2,5- di(tert-butyl)-1, 4 hydroquinone (DBHQ). This results in certain biochemical and functional adaptations with respect to cellular Ca2+ homeostasis and SERCA pumps in the resistant cell lines. In this application, we propose a series of detailed molecular biological studies o the SERCA pumps present in the resistant cell lines in order to dissect the potential range of adaptations that can occur within them with respect to expression and function under such specific selective pressure. These studies will yield novel information regarding mechanisms controlling altered (and potentially pathologic) Ca2+ homeostasis, which are relevant and important to understanding disease states associated with abnormalities in Ca2+ homeostasis.